Evolution by Means of Natural Selection

Charles Darwin Born to a wealthy family in England in 1809. Had intended to study medicine but later decided to study divinity (religion). Joined the crew of the HMS Beagle in 1831 on a five year voyage as a naturalist. Most important stop on their voyage was the Galapagos Islands. Published a book called On the Origin of Species by Means of Natural Selection in 1859.

Darwin’s Work on the Galapogos Islands While on the Galapogos Islands, Darwin studied three types of animals: turtles, marine iguanas, and finches (a type of bird). Darwin took the information he recorded about his observations and formulated his concept of evolution by means of natural selection.

Darwin’s Observations Turtles – different island, different habitat, different shell shape. Marine Iguanas – adapted to go under water and eat algae off of rocks. Finches – different island, different habitat, different beak shape

Darwin’s Conclusions Darwin noticed the finches on each of the different islands had greatly diversified. The finches had different beak structures as well as different feeding habits. From these observations, Darwin concluded that speciation had occurred. Remember that speciation is the process by which different groups of an organism evolve independently from one another, ultimately becoming a different species. This was due to geographic isolation

Darwin’s Conclusions So each island had finches with different adaptations. Darwin suggested that natural selection was the process that caused these adaptations which lead to speciation.

Preconditions of Natural Selection The process of natural selection has several preconditions that must be met: The members of a population show variation. More individuals are born in a population than die. Some individuals inherit adaptive characteristics that favor their survival and reproduction. >

What is Natural Selection? Natural selection is also known as survival of the fittest. It is the mechanism of change in a population. Population = same species living in the same area at the same time that can interbreed. What do you think will happen to this population of beetles?

How Natural Selection works…. Well adapted individual going on with “life”. More likely to survive Will more than likely live long enough to reproduce Reproduces and passes its genes on to its offspring. More of that trait seen in future generations of that population.

Big Ideas to Remember about Natural Selection Can not be seen immediately Populations evolve; individuals do not evolve. This is the mechanism of change in a population.

So tell me what evolution is…. Evolution is a change in the gene pool of a population over a period of time. How does this relate to natural selection? Natural selection is the mechanism that causes the change in the gene pool.

In the end….. Those organisms best capable of obtaining resources necessary to survive and reproduce are those with the greatest fitness. They are the ones best adapted for their environment. This is why natural selection is often referred to as survival of the fittest. The trait that determines whether an organism is fit varies from population to population.

Descent with modification Beetles of a different color Most of the beetles in the population (say 90%) have the genes for bright green coloration and a few of them (10%) have a gene that makes them more brown. Some number of generations later, things have changed: brown beetles are more common than they used to be and make up 70% of the population.

Is there any other type of selection? Why yes, there is. It is called artificial selection. Artificial selection occurs when people select specific traits that are favorable in a specific animal, find the animals with those traits and breed those animals.

Example of Artificial Selection Suppose you are a dairy farmer. You breed your cattle for the best milk. Milk that is high in fat content is the most marketable. You breed the cows that are from a lineage that produces milk with a high fat content. Eventually, all of the cows you raise will produce milk that has a high fat content and you will have a very marketable product.

So summarize the modern theory of evolution…. The modern theory of evolution includes all of the following concepts: Competition among the members of a population. All of the members are competing for the same resources to survive long enough to reproduce and pass on their genes to their offspring. Natural Selection (also known as Survival of the Fittest) Descent with modification Darwin’s theory also suggests that species change over time.

So what other evidence of evolution exists? Well…. Scientists have looked at the following: Patterns in the fossil record Similar anatomy Biochemical similarities – comparing DNA and proteins All of these are used to suggest common ancestory.

Fossils…. A fossil is the remains of a once living organism. They can be…. bones, footprints or imprints. The history of life on Earth can be shown by fossils preserved in rocks. This record shows: How species changed over time If a species went extinct

How can you tell the age of a fossil? The age of a fossil can be determined in one of two ways: Absolute age Relative age Absolute age can determine the exact age of the organism. This is based on the half life of the carbon left in the fossil. Half life = the amount of time it takes for half of a substance to decompose.

Amount of Parent Material Amount of Daughter Material Half Life Example Amount of Parent Material Amount of Daughter Material Years Passed 200 grams 0 grams 5730 11460 17190 22920 28650 3.125 grams 96.875 grams 34380

Relative Age Remember that relative age simply tells you whether something is older or younger than the organism you are comparing it to. We can determine relative age by looking at the layer in which a fossil is found. The older fossils are found in layers below the younger fossils.

Similar Anatomy We use similarity in anatomy and embryos to show evidence of common ancestory.

Adaptations… what are they? An inherited trait that increases the chances of survival. They can be… Anatomical – like quills on a porcuipine Physiological – the different ways different plants carry out photosynthesis Behavioral - Animals hunting in groups

Mimicry…. Don’t copy me!!!! Mimicry occurs when one organism looks like or behaves like another of a different species or something in that organisms surroundings.

Resistance… I just couldn’t resist!! Sometimes bacteria do not respond to the antibiotics prescribed to kill them. This is due to a concept known as antibiotic resistance. Here’s what happens…

It can happen in pesty insects too!!! Sometimes it happens in some insects, pests. Here’s a closer look…..